In E. coli, tyrosine tRNA1 is encoded by a complex locus called tyrT. Two sequences encoding mature tRNA are separated by a 208 bp spacer sequence and sequences comprising the distal region of the locus code for a small highly basic protein. The distal region is also characterized by a 178 bp sequence that is repeated 3.14 times and commences with the lst 19 bases of the mature tRNA sequence. Transcription of this locus is being studied both in vitro and in vivo. A rho-dependent transcription termination site is located in the second repeat unit. The pattern of transcription products suggests the existence of a graded set of termination sites. A number of mutants in the tyrT promoter have been sequenced and a functional analysis is being continued.